1. Field of the Art
This invention relates to a flexible channel to be fitted in an endoscopic insertion portion to serve as a passage of forceps or other surgical or medical instruments, for insertion of operating wires or other components, or as a passage for sending a fluid into or out of a body cavity.
2. Prior Art
Generally, the so-called biopsy channel is provided in an endoscopic insertion portion for introduction of forceps or other treating instruments into a body cavity. The biopsy channel of this sort is extended forward from an manipulating head assembly as far as a fore distal end of an elongated insertion portion. In case the endoscopic insertion portion has a flexible section in part of its length, the biopsy channel needs to have a flexible structure in that section. Therefore, usually a biopsy channel is formed by the use of a flexible tube of a soft or pliable synthetic resin material and fitted in an endoscopic insertion portion in such a way that it is free from buckling when the insertion portion is bent or when it is pressed by other component parts which are fitted in the insertion portion. In order to retain the shape of the flexible tube, it has been a wide practice to wind a metal wire like a steel wire helically around the outer periphery of the flexible tube as a reinforcing coil. In this regard, normally a reinforcing metal wire is wound around a flexible tube in a predetermined pitch, usually in a wide pitch. In some cases, in order to hold helices of a reinforcing metal wire in predetermined position without increasing the diameter of the flexible tube, a helical groove is formed on the outer periphery of the flexible tube to anchor the reinforcing metal wire therein.
Shown in Japanese Laid-Open Patent Application H5-184533 is a method for forming a helical groove on the outer periphery of a flexible tube, which has thus far been in use in the art. In this prior art method, a blank flexible tube is set on a rotating means, and outer peripheral surface of the flexible tube is heated to a softened state while the flexible tube is rotated by the rotating means. In this state, a rotating die is pressed on the softened outer peripheral surface of the flexible tube and moved in the axial direction of the flexible tube to form a helical groove around the outer periphery of the flexible tube in a predetermined pitch. A reinforcing metal wire is then anchored in the helical groove to form a reinforced flexible channel.
An operator who grips an endoscopic insertion portion in his or her hand often tends to twist rod at the time of introducing the insertion portion into a body cavity or at the time of turning a distal end portion of the insertion portion into a different direction. When an endoscopic insertion portion is handled in that way, a biopsy channel which is fitted in the insertion portion is also subjected to a twisting force. A reinforcing coil in a helical groove around a flexible tube of the biopsy channel is not securely fixed in the groove, so that application of a twisting force may cause positional deviations to the reinforcing coil in the groove, leaving the coil in an instable state. In this connection, by the use of a reinforcing coil with an inside diameter which is smaller than a root diameter of the helical groove, the reinforcing coil can be pressed against root portions of the helical coil more tightly and anchored therein in a more stabilized state. However, since root portions of the helical groove on the flexible tube is very small in wall thickness, so that inward deformations may occur to these portions under the pressing force exerted by the reinforcing coil, forming inward protrusions on the inner periphery of the flexible tube to such a degree as to hinder insertion of forceps or other medical treating instruments.